This invention relates generally to a method and device for protecting underground utility conveyances from damage such as might be caused by excavation.
It is well known that utilities bury their pipes and/or cables (hereinafter, xe2x80x9cconveyancesxe2x80x9d) underground to protect the conveyances from the elements, i.e., wind, rain and sunlight, as well as for cosmetic reasons. However, because the conveyances are hidden from view, they are susceptible to severing, breakage, puncturing, or other damage due to excavation. It is well known that in order to avoid damage caused by excavation utilities often record the location of such conveyances and sometimes mark said conveyances with stakes, posts, or other types of marking means.
It is also well known that utilities have used electromagnetic signaling to locate underground conveyances in order to avoid damaging them during excavations. As set forth in U.S. Pat. No. 5,644,237, incorporated herein by reference, typically the utility applies an alternating current signal at a unique frequency to each buried conveyance either directly or to a separate wire buried adjacent to the conveyance. A technician seeking to locate the conveyance employs a cable-locating detector such as a radio frequency (RF) receiver tuned to the frequency of the signal impressed on the conveyance. Because of stray electromagnetic signals radiated by other underground conveyances lying nearby, the technician may not be able to locate the exact position of the conveyance of interest. As a result, the technician may have to physically uncover the buried conveyance in order to establish its exact location
U.S. Pat. No. 5,438,265, incorporated herein by reference, discloses a cable-locating device that utilizes an RF detector and a viewing mechanism, such as a television camera or the like, to precisely locate a buried utility conveyance. Such an approach is complex and expensive and requires a means of excavation provided within the device for removing the earth in the vicinity of the cable to allow observation by the viewing mechanism.
Another approach that has been employed in the prior art is to associate permanent magnets with a fiber optic cable as by providing magnets on a tracer tape buried separately along with the cable in order to assist in locating and tracing the cable. U.S. Pat. No. 5,006,806, disclosed herein by reference, discloses an apparatus for marking, locating, tracing, and identifying hidden conveyances by providing the conveyances with elongated, permanent magnet identifier devices having magnetic fields that may be detected at a distance from the objects. However, this approach has several disadvantages, including the possibility that the tracer tape will be installed improperly and thus will not be detected. The limited distance at which the tape can be detected and the inability to reliably distinguish the weak magnetic field of the magnets from magnetic fields associated with ferrous pipes, for example, that may be buried in the same area is also a significant drawback.
U.S. Pat. No. 5,194,812, incorporated herein by reference, discloses a method of identifying a cable buried underground in which an alternating current signal is applied to the cable and the magnetic field due to the current signal is detected using a magnetic field sensor brought into proximity with the cable.
However, the foregoing approaches have several disadvantages, including interference of electromagnetic signals caused by other conveyances and objects within the earth and the inherent fallibility of sensing devices. In addition, the need for sensing equipment is a drawback because of cost and because excavators may not always be equipped with the proper sensing equipment for a given system.
It is also well known to install plastic warning layers above buried conveyances to alert excavators to their presence. However, such plastic warning layers are often ignored by excavators or equipment operators, who dismiss the plastic layers as refuse or simply buried garbage. Often, the plastic warning layers are simply punctured by the excavating equipment and remain buried because they do not come to the surface or become more visible as a result of excavation. Thus, there is the need for a simplified, low-cost device and method for preventing damage to underground conveyances.
The present invention provides a new device and method for preventing damage to buried hidden objects such as underground conveyances, namely cables, pipes, tubes, ducts, conduits and the like.
The present invention provides a device which provides color and texture contrast to backfill, is highly reflective and provides a means for excavating equipment to bring the device to the surface and to the attention of the equipment operator to alert the operator to the presence of a buried conveyance.
In accordance with one of the broader aspects of the invention, an elongated carrier material is filled with a suitable material and said carrier material further comprises a webbing around or within said carrier. The device comprising essentially the carrier, the suitable material and the webbing is disposed along the axis of an elongated hidden object such as a utility conveyance after said conveyance is installed in the ground and preferably after installing a suitable amount of backfill, approximately six inches to four feet of backfill, the device is installed directly on the backfill along the longitudinal axis of the conveyance and is typically lain along the entire length of the conveyance. The carrier of the device is typically any material suitable for carrying the material to be contained therein, including but not limited to plastic sheeting, plastic sacking or a suitable fabric, cloth or cloth-like material and the like. The carrier can alternatively comprise PVC pipe, lightweight metal tubing or the like. The fill material typically comprises crushed or broken glass but optionally may comprise colored or uncolored gravel or a suitable substitute. The webbing material typically consists of wire or woven wire but may comprise high-strength PVC netting or a suitable substitute such as but not limited to natural or synthetic woven or unwoven fiber. It is contemplated that the device is placed far enough above the underground conveyance so that the device takes the impact of any excavation equipment such as a backhoe or a trencher before such equipment contacts the underground conveyance. The device therefore acts as a warning layer that alerts excavators to the presence of an underground conveyance. In a most preferred embodiment, the device is a wire-wrapped plastic sack containing colored crushed glass. The device provides color and texture contrasts to soil and backfill, is highly reflective, is readily noticeable in its packaging, and the wire wrapping readily snags on the teeth of a backhoe to bring it up to alert the equipment operator before digging continues downward into the excavation toward the valuable underground conveyance. The wire wrap may also be located by electromagnetic sensing equipment.